1. Field of the Invention
An aspect of the present invention relates to an image scanning device and an image forming apparatus including the image scanning device.
2. Description of the Related Art
Generally, in an image scanning device, multiple image sensors are arranged alternately (i.e., staggered) such that the end portions of adjacent image sensors partly overlap each other in the main-scanning direction. Compared with a case where one image sensor with a large width is used, using mass-produced, inexpensive image sensors with a small width (e.g., A4 or A3 size) makes it possible to reduce the costs of parts of an image scanning device. However, using multiple image sensors makes it necessary to adjust the mechanical alignment of the image sensors and complicates image processing (e.g., it is necessary to combine images obtained by the respective image sensors). Also, if the positional relationship between image sensors changes due to, for example, thermal expansion, images obtained by the image sensors may be misaligned.
Various technologies have been proposed to solve or reduce the above problems. For example, Japanese Patent Application Publication No. 2004-336201 discloses a technology where multiple image sensors are joined together via fitting parts provided on the housings of the image sensors so that “alignment points” of the image sensors can be easily aligned. Here, “alignment points” of image sensors indicate points on the image sensors at which the image sensors are aligned with each other.
As another example, Japanese Patent Application Publication No. 2003-87504 discloses a technology where materials with the same coefficient of linear expansion are used for the housing of an image sensor and a supporting frame to prevent deformation of the image sensor fixed to the supporting frame due to thermal expansion.
Also, Japanese Patent Application Publication No. 2002-314768 discloses an image scanning device including a temperature sensor for detecting the temperature near image sensors. In the disclosed image scanning device, scanning start pixels and scanning end pixels at the seam between the image sensors are controlled according to temperature changes to compensate for misalignment of the image sensors due to the temperature changes.
Also, Japanese Patent Application Publication No. 5-336301, Japanese Patent No. 2572307, and Japanese Patent Application Publication No. 2005-198254 disclose a technology where sensor substrates of adjacent image sensors are connected to each other to reduce the misalignment of the image sensors in the main-scanning direction due to thermal expansion.
Further, Japanese Patent No. 3784249 discloses an optical writing device where multiple light-emitting element arrays are staggered in the main-scanning direction and connected to each other in a manner similar to Japanese Patent Application Publication No. 5-336301, Japanese Patent No. 2572307, and Japanese Patent Application Publication No. 2005-198254 in order to reduce occurrence of undesired lines in an image at the seams between the light-emitting element arrays.
However, the disclosed technologies have disadvantages as described below. In the technology disclosed in Japanese Patent Application Publication No. 2004-336201, misalignment of the alignment points of image sensors caused by thermal expansion is not taken into account.
In the technology disclosed in Japanese Patent Application Publication No. 2003-87504, the coefficient of linear expansion of the sensor substrate is not taken into account. Therefore, when multiple image sensors are staggered, alignment points of the image sensors may be misaligned due to thermal expansion.
With the image scanning device disclosed in Japanese Patent Application Publication No. 2002-314768, the control accuracy may be reduced by the difference between the actual changes in image sensor sizes due to temperature changes and the changes in image sensor sizes estimated based on the temperature detected by the temperature sensor. Also, the disclosed configuration requires a temperature sensor and a control unit and therefore increases production costs.
With the technology disclosed in Japanese Patent Application Publication No. 5-336301, Japanese Patent No. 2572307, Japanese Patent Application Publication No. 2005-198254, and Japanese Patent No. 3784249, it is necessary to fix connecting parts to the sensor substrates with an adhesive or screws. This may increase the risk of damaging the sensor substrates.